This invention pertains to the technology sector of machine tools that perform very high-speed (at sometimes even more than 200,000 rpm) drilling, milling, grinding, etc. operations.
One of the more specific applications for such machine tools is that of working support plates for printed circuits.
More particularly, this invention pertains to an array of electromagnetic motors that are prearranged in a machine in order to ensure the rotational and/or axial movement of a tool-carrying sleeve. In his European patent application number 99 204 130.1, the same applicant previously described an innovative array in which the movable magnets of a linear motor are attached to the outside of the tool-carrying sleeve, while the stator coils are attached to the inner surface of a hollow member that is coaxially external with respect to the tool-carrying sleeve itself.
While offering valid advantages, this solution, which moreover is implemented in various ways in other examples according to the state of the art, has the drawback that, owing to the above-mentioned high speed of rotation, the movable magnets are subject to stress from elevated centrifugal forces that can, in turn, cause some or all of the magnets to be detached from the substrate to which they are attached. Even the detachment of individual sintered particles can impair operations since said particles remain stuck in the air gap that is present between the movable magnets and the fixed stator coils, thereby exerting a dangerous and damaging xe2x80x9cgrindingxe2x80x9d action on the component parts.
Because the technology of this field of endeavor is focused on achieving ever higher working speeds, the inventor of this invention considered it necessary to look for a solution that would avoid the risk of drawbacks similar to those described above. To this end, he has thought up a new way of arranging the various component parts of an array that is composed of the electromagnetic motors. According to the invention, in fact, as will be further described below, the magnets are attached coaxially to the inside of a robust hollow tube that is integral with the tool-carrying sleeve itself, while the coils are attached to the outside of a shaft that is inserted coaxially into said hollow sleeve, whereby said shaft is held firmly in place during operation in order to perform its stator function.
This solution ensures that the magnets are pushed by centrifugal force against the inner surface of said hollow tube, whereby said centrifugal force exerts a supporting and opposing action that prevents the magnets from moving in the radial direction and prevents individual particles thereof from becoming detached from the magnets in the radial direction.